1. Field of the Invention
The present invention relates to a fuel supply device.
2. Description of Related Art
A fuel supply device has an electric pump to supply fuel to an internal combustion engine. A pressure of the supplied fuel is controlled based on operation state of the engine so as to reduce fuel consumption of the engine. For example, when the engine has an idling operation, the pressure of the supplied fuel is lowered so as to reduce power consumption of the pump. In contrast, when the engine has a high-load operation, or when the engine is started, the pressure of the supplied fuel is raised so as to increase an output amount of the engine. Thus, fuel mileage can be improved.
JP-A-2007-263032 discloses a fuel supply device using a pair of electric pumps. Specifically, the fuel supply device includes a primary pump, a backpressure control pump, and a pressure regulator. The pressure regulator has a fuel chamber and a backpressure chamber. The fuel chamber communicates with a passage to which the primary pump supplies fuel. The backpressure chamber communicates with a passage to which the backpressure control pump supplies fuel.
When a fuel pressure in the fuel chamber becomes higher than a regulation pressure corresponding to a fuel pressure in the backpressure chamber, fuel is discharged out of the fuel chamber. The fuel pressure in the fuel chamber is controlled to have the regulation pressure, and fuel having the fuel pressure is supplied to the engine.
A pressure of fuel supplied to the engine is set by a valve-opening pressure corresponding to the fuel pressure in the backpressure chamber. The fuel pressure in the backpressure chamber depends on a pressure of fuel discharged out of the backpressure control pump. Therefore, the discharge pressure of the backpressure control pump is required to be accurately controlled so as to accurately control the pressure of fuel supplied to the engine. However, the discharge pressure of the backpressure control pump is easily changed by disturbance such as a voltage variation of a power source to supply electric power to the backpressure control pump. JP-A-2007-263032 fails to disclose a control method to cancel the change of the fuel pressure.